diff --git a/R/diann-R.R b/R/diann-R.R
index ba7dbbd..20135d7 100644
--- a/R/diann-R.R
+++ b/R/diann-R.R
@@ -35,7 +35,7 @@ pivot <- function(df, sample.header, id.header, quantity.header) {
   piv <- as.data.frame(dcast.data.table(x, as.formula(paste0(id.header,'~',sample.header)), value.var = "value")) 
   rownames(piv) <- piv[[1]]
   piv[[1]] <- NULL
-  piv <- piv[order(rownames(piv)),]
+  piv <- piv[order(rownames(piv)), , drop = FALSE]
   as.matrix(piv)
 }
 
@@ -45,7 +45,7 @@ pivot_aggregate <- function(df, sample.header, id.header, quantity.header) {
   piv <- as.data.frame(dcast.data.table(x, as.formula(paste0(id.header,'~',sample.header)), value.var = "value", fun.aggregate = function(x) max(x, na.rm=TRUE))) 
   rownames(piv) <- piv[[1]]
   piv[[1]] <- NULL
-  piv <- piv[order(rownames(piv)),]
+  piv <- piv[order(rownames(piv)), , drop = FALSE]
   piv = as.matrix(piv)
   piv[is.infinite(piv)] <- NA
   piv
@@ -172,4 +172,4 @@ diann_save <- function(x, file, row.names=F) {
 
 .onUnload <- function(libpath) {
   library.dynam.unload("diann", libpath)
-}
\ No newline at end of file
+}